The present invention is directed to a clutch which is fitted on the outlet of a main motor of a machine for use for converting plate-shaped elements, such as strong paper, flat paperboard or sheets of corrugated board. On account of the power being applied, such a clutch is usually actuated by means of a fluid acting on a membrane moving along an adopted axis of the clutch assembly, which assembly is provided with the friction surfaces. Another feature of the clutch is that the coupling system used between the clutch element and its rotary axle is elastic.
By way of principal, a clutch includes a flange permanently fitted on a first shaft or flywheel and a plate holding a friction disk which is fitted on a second shaft is positioned coaxially to the first shaft or flywheel in such a way that the plate is fixed for rotation with the second shaft but can be axially moved with regard to the second shaft. As may be easily understood, the clutching-in action consisted of shifting the plate towards the flange until the friction disk of the plate makes contact with the flange. The friction forces occurring when the friction disk and flange are in contact with one another enables the transmission of the torque from the first driving shaft or flywheel to the second driven shaft, or in an opposite direction, if the second shaft is the driving part. The permanent position of the clutch is usually insured by springs or other pullback means whereas the temporary position is obtained by means of a mechanical device of purely kinematic execution or else involves a fluid, such as compressed air or hydraulics. For instance, in an automobile clutch, which is supposed to remain permanently engaged, radial springs with their seats on a hub sliding along the second shaft are connected to pivots on the inner periphery of the housing to exert pressure against the side of the plate to urge it towards the flange connected to the motor. When the pedal is actuated, the hub is shifted in a direction which causes the springs to pull the plate away from the flange and move it along the second axle or shaft to disengage the clutch.
In the event of large power transfers put to work, it might be useful to double the clutch, which would then include two flanges held in parallel and apart from one another by a peripheral distance piece. The assembly is such that the two plates are coaxially fitted on a first shaft or flywheel. This clutch includes an addition of a plate and counter-plate, which are fitted coaxially on a second shaft between the two flanges. As a rule, the plate and counter-plate are close to one another when in a declutched or disengaged position by appropriate springs whereas pistons are positioned between the plate and counter-plate for the purpose of moving them apart from one another as requested when engaging the plates with the surfaces of the flanges. Hence, if trouble appears on the machine, especially so on a hydraulics circuit, a pull-back means will automatically disengage the clutch.
Both examples mentioned above show the importance of easy sliding of the plates that hold the clutch friction disk on a rotary shaft. This problem has been resolved by cutting a row of lengthwise teeth or splines into the periphery of the shaft. Teeth matching those on the shafts will be cut into the inner circular section of the plate or plates. In this way, an insertion of the plate or plates along the shaft can easily occur with the teeth of the plates meshing with the teeth of the shaft. In this way, the plate is fixed when rotated but free to move axially along the shaft.
Any difficulties likely to arise with this arrangement are reduced by high-precision rectification of the teeth after their cutting in order to eliminate, if possible, any backlash. Moreover, the support of the second shaft is carefully greased in order to reduce as much as possible the friction forces occurring in this area during the axial movement of the plate element along the shaft.
Even though satisfactory up to a medium power rate, this mode of coupling the plate on the shaft becomes inadequate with high potential clutches resulting initially in teeth knocking against one another and leading to backlash. Once this backlash has become sufficiently large, it will cause jarring when the clutches are engaged with vibrational-like shocks propagated harmfully through the whole machine. The backlash area will then develop contact erosion which will considerably increase the frictional forces to be overcome when having the plate shifted by the actuating means, such as the piston or a fork, or by a reactive pull-back means. This appearance of the increased friction will result in a slower clutch response to a command which is particularly dangerous in the event of an emergency disengagement of the clutch.